Specifying Chemical Components and Physical Properties

The structure of the flowsheet is now completely specified. Next, we must define the chemical components involved in the separation and specify what physical property package is to be used. Chapter 1 discussed many aspects of choosing a physical property relationships, so that an accurate representation of reality is used. 

A simple binary separation of propane from isobutane is used in the numerical example considered in this chapter. The VLE relationships for most hydrocarbon systems are well handled by the Chao-Seader correlation, so we select that package. 

A couple of preliminary items should be done first. In the middle of the window, there are two boxes in which we can specify the units to be used in the simulation. Figme 3.15 shows the standard three alternatives ENG (English engineering), MET (metric), and SI (Systeme International). We will use SI units in most of the examples in this book because of the increasing importance of our global economy. However, we will make one departure from regular SI units. In the SI system, pressures are in pascals (N/m ), which are quite inconvenient for most chemical processes because typical pressme are very large numbers in pascals (1 atm = 101,325 Pa). Therefore, we will use pressmes in atmosphere in most of the examples. However, make sure that you select the correct units when you enter data. 

The second preliminary item is to indicate what properties we want to see for all the streams. The defaults do not include compositions in mole fractions, which are very useful 

A list of components is opened at the bottom of the window (Fig. 3.18). Click PROPANE and click the Add button at the bottom of the window. Repeat for ISOBUTANE and click Close. 

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